1. Field of the Invention
The present invention relates to a driving control apparatus of an automobile and, in particular, to a apparatus for controlling the steering angle, braking force and driving force of each wheel so as to improve the stability in driving of the automobile.
2. Description of the Prior Art
Conventionally, there has been a strong cry for an automobile with improved driving stability for safe driving. For instance, when an automobile is turning at an extremely low speed, the front wheels are steered corresponding to the driver steering angle of the steering wheel. The vehicle turns according to the angle of the front wheels as thus steered. In such a state of turning while traveling, the direction of the steered wheels roughly agrees with the wheels' traveling direction and turning of the vehicle can be done stably. However, when turning is done with the vehicle's speed high and the centrifugal force acting on the vehicle is accordingly high, and vice versa, or with a driving force or braking force acting in the event of a sudden acceleration, or deceleration respectively, the steering direction of the wheels is markedly deviated from the traveling direction thereof, and the vehicle cannot travel in the direction attempted by the driver.
Hence, there was a problem of loss of traveling stability when a sudden turning was made as well as in the event of a sudden acceleration or deceleration made while doing a normal turning.
However, conventionally, there has been no known technique for solving such a problem. Hence, with a conventional 4-wheel steering vehicle an attempt is made to improving the traveling stability by detecting the handling steering angle of the steering wheel with an angle detector attached to the revolving shaft of the steering wheel so that proper control is made on the basis of the signals transmitted by the aforementioned detector. With a 4-wheel steering vehicle which requires complicated control, such arrangements are made for proper control as providing the speedometer with a speed detector, providing a lateral accerometer near the vehicle's center of gravity for detecting (determining) the magnitude of centrifugal force acting on the vehicle's center of gravity or providing a yaw-gyro detector near the center of gravity for detecting the magnitude of yawing (moment), and having the handling steering angle of the steering wheel controlled according to the detection signals from the speedometer, lateral accerometer and yaw-gyro detector.
Another problem is inability to generate the component for each wheel of the centripetal force corresponding to the centrifugal force acting on the vehicle due to skidding of its wheels, this resulting in deterioration of the vehicle's traveling stability. In order to solve this problem, known control devices of the skid control type are so designed that the braking force or the driving force of the skidding wheel is weakened to prevent skidding. The judgment whether a wheel is skidding or not is done by providing each wheel with a number-of-revolutions detector for detecting the number of revolutions per unit length of time and determining the mean number of wheel revolutions from that of each of the 4 wheels and, if the number of revolutions of any of the 4 wheels should be markedly different from the mean number of wheel revolutions, that is, if the number of revolutions of any braking wheel is lower than that of the mean number of revolutions, it is judged that the particular wheel is skidding.
The aforementioned skid control consists in controlling each tire not to unduly skid and expecting that the natural capability of the tire generates a proper cornering force and is not of the nature to positively control the traveling direction of each wheel. Such skid control is feasible with the aforementioned 4-wheel steering vehicle, indeed, but even in such prior art there are influences of other various factors involved and the optimum steering direction with the deviation of wheel's traveling direction taken into due consideration cannot be determined. As such influences are cited, among others, (a) influence of the tire, that is, change of grip performance resulting from changing tires, of the pneumatic pressure, of the degree of tire wear and the tire temperature during traveling and of the balance of the individual wheels with their tire grips dependent thereupon, (b) influence by the vehicle's conditions such as the condition of suspension and shifting of the center of gravity during traveling, (c) influence by the aerodynamic force, that is, how strong an aerodynamic force is acting on what part of the traveling vehicle and in what direction, (d) influence by the road conditions, that is, by the change in friction coefficient between the tire of each of the 4 wheels et cetera, and all these influences, (a)-(d), have to be taken into due consideration. These influences, (a)-(d), all influence the traveling stability of the vehicle, but it is difficult to detect, compute and control all of them. Accurate and simple control with all the aforementioned factors, (a)-(d), influencing the traveling stability is feasible by detecting the traveling direction of each wheel and determining its deviation from the steering direction.